Cystic fibrosis (CF) is a genetic disease caused by loss of cystic fibrosis transmembrane conductance regulator (CFTR). The disease involves many organs, and lung disease is the current major cause of morbidity and mortality. Gene transfer offers the potential to express CFTR in the lungs of patients and thereby slow or prevent disease progression. Yet despite outstanding research progress, we still lack answers to many crucial questions. A major impediment to progress has been the lack of an animal model that replicates disease typically found in humans. To circumvent limitations of current animal models, we have produced CFTR-/- and CFTRAF/- pigs. Newborn animals exhibit defective CI'transport and replicate abnormalities in newborn humans. Our preliminary data suggest that CFTR-/- pigs may also develop respiratory disease like humans. We will use this novel model to address questions key to CF. Aim 1. Will intestinal expression of CFTR prevent meconium ileus in CFTRAF508/- pigs? To answer this question, we will generate CFTRAF508/- pigs carrying a transgene expressing CFTR in the intestine. The resulting animals may be of value to other projects in the program, and the results may shed light on the underlying pathogenesis of meconium ileus and distal intestinal obstruction syndrome. Aim 2. Do genetic modifiers influence the clinical phenotype of CFTRAF508/AF508 pigs? We will cross our pigs to genetically diverse strains of pigs and ask how the CF phenotypes are altered. Discovering phenotypic changes could help identify pathways that modify the AF508 mutant protein or affect manifestations of the disease, thereby revealing novel therapeutic targets. Aim 3. When is CFTR expression required to alter the CF phenotype? We will generate CFTRAF508 pigs that express CFTR under control of an inducible promoter to answer key questions. Will CFTR expression in utero prevent disease in newborns? Will epithelial CFTR expression that begins after birth prevent lung disease? Will CFTR expression treat or slow the progression of established ainway disease? The answers will serve as a benchmark to guide therapeutic strategies including gene transfer.